1. Field of the Invention
The present invention relates to a substrate for a display panel where a drive signal is applied through a plurality of wiring electrodes drawn out from the inside to the outside of a container, and to an image forming apparatus such as a display device using the same.
2. Related Background Art
Conventionally, as display devices, the following are known: gas discharging type ones such as PDPs (plasma display panels); and electron beam irradiating type ones such as FEDs (field emission displays) where light emitting members are irradiated with electron beams. As electron-emitting devices for electron beam irradiating type displays, two kinds are known: thermionic source type ones; and cold cathode electron source type ones. The latter type includes field emission type devices (FE type devices), metal-insulator-metal devices (MIM devices), and surface conduction electron-emitting devices.
The above-mentioned surface conduction electron-emitting devices have an advantage that a number of devices can be formed over a large area since they are simple in structure and easily manufactured, and thus, various kinds of applications of the devices are under research to make full use of the advantage. The applications include those to an ion beam source, and to a display device such as an image forming apparatus. As an example, the present applicant proposed in Japanese Patent Application Laid-Open Nos. 2000-251778 and 2000-251802 an image forming apparatus in which an electron source plate where multiple electron-emitting devices are connected to wirings in a matrix and an opposing substrate having a phosphor disposed therein are laminated together to form a high vacuum container (display panel).
However, when the above-mentioned image forming apparatus is constructed in which an electron source plate where multiple electron-emitting devices are connected to wirings in a matrix and an opposing substrate having a phosphor disposed therein are laminated together to form a high vacuum container (display panel), and when the area of the image forming apparatus is made larger and the quality of the image forming apparatus is made higher, the following problems arise.
First of all, as a wiring material, thick film paste including metal and a glass material is used to satisfy required wiring resistance. However, when higher definition is tried to be achieved in order to make higher the quality of the image forming apparatus, it is necessary to make the wiring width sufficiently small in a display area. It is desirable for a high definition display device to have the wiring width of about 70 μm or less in order to be sufficient for general use, though, specifically, depending on the specific purpose of using the display device.
Further, as in the case of a surface conduction electron-emitting device disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2000-251778, when an electron source plate is used which is configured such that gaps between opposing electrode pairs (device electrodes) are disposed in parallel with column (Y) direction wirings (lower wirings) and such that electron-emitting regions are formed as lines substantially in parallel with the Y direction wirings (lower wirings), since the trajectory of emitted electrons must be controlled, it is desired that the edge height of the Y direction wirings is sufficiently high (for example, about 14 μm) in the display area. The sufficient height is also necessary in order to sufficiently decrease the resistance value of the wiring as described above.
As used herein, the term “display area” means an orthogonal projection area of an image forming member such as a phosphor onto a wiring substrate. When a display panel is formed by disposing the above-mentioned electron source plate and a transparent substrate, having a phosphor formed therein, so as to be opposed to each other, an area on the electron source plate (wiring substrate) opposed to the phosphor is the orthogonal projection area of the image forming member (phosphor) onto the wiring substrate.
As a result of consideration of specific means for materializing formation of wirings having a minimum wiring width and a sufficient height (thickness) in order to attain both higher definition and decreased resistance of matrix wirings in the display area, we found it was preferable for the wiring formation method to be changed from conventional screen printing to photolithography using a photo paste material. More specifically, when wirings are conventionally formed using printing, since the cross section shape is a smooth hemisphere, it is difficult to materialize both a sufficient height and a high definition wiring width. As a wiring shape materializing both a narrow width and a sufficient height (thickness), a rectangle having abrupt edges is preferable. We consider that, in order to form wirings in such a shape, photolithography using a photo paste material is preferable.
However, when the thickness of the photo paste material is increased to secure an edge height of the wirings for the purpose of decreasing the wiring resistance and controlling the trajectory of electrons emitted from the electron-emitting devices, the edges of a pattern are curled (scooped) and the plate is easily subject to cracks, and thus, a problem can arise in that the airtightness is decreased (a leak path is formed) at the outer periphery of the display area where the panel is seal-bonded.